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Advances in photoelasticity applied to biomechanical problems
Abstracts of the Fourth Meeting of the European Society of Biomechanics THREE-DIMENSIONAL
STRUCTURAL
ANALYSIS
533
OF THE LOCOMOTOR
SYSTEM
V. NIKOLI~, M. HUDEC, M. MAROTTI, A. Jo and A. LOVRI~:(Department of Anatomy, Zagreb, Yugoslavia) Computerized tomography (CT) gives a quantified geometrical and structural picture of the cross-section of a body part, including muscles, tendons and ligaments. We investigated, by use of serial, transversal CT sections, the spatial distribution and position of the biomechanically important constituents on the living human locomotor system. Previously reported computer programs give the mechanically equivalent reduced bone crosssections and their moments of inertia. For certain positions and movements of the human body and extremities, the external forces can be determined quite accurately and, therefore, the internal resulting forces too. By a computerized structural analysis of a part of the extremity structure, we computed the tensile force intensities in muscles and tendons, and the adequate compressive forces in the bone, using the condition of the minimal internal energy. MINIMUM-VARIANCE ROTATION
ESTIMATION
IN JOINT BIOMECHANICS
OF INSTANTANEOUS
CENTRES AND AXES OF
FROM NOISY LANDMARK
MEASUREMENTS
H. J. WOLTRING, A. DE LANGE and R. HUISKES (Laboratory for Experimental Orthopaedics, University of Nijmegen, The Netherlands) The planar centre and spatial axis of rotation are useful quantifiers of biomechanical joint movement since they enable us to relate joint kinematics to joint geometry; furthermore, they allow the definition of suitable reference points for net joint moment assessment in dynamic movement studies. The instantaneous centre and axis of rotation (ICR and IAR, respectively) have usually been estimated from theirfinite counterparts; these are excessively sensitive to errors in measured landmark co-ordinates. The present paper treats sampled landmark data as measurements on a continuous, bandwidth-limited movement process. Through suitable low-pass filtering and differentiation techniques, largely unbiased estimates of the ICR and IAR can be obtained with a substantially higher accuracy than would be feasible through traditional, finite approaches. COMPUTERIZED TOMOGRAPHY TO FINITE ELEMENT
AND PATTERN RECOGNITION ALGORITHM MESH GENERATION OF BONE STRUCTURES
J. P. COYE~E (Universite Catholique de Louvain, Louvain-la-Neuve,
AS AN AID
Belgium)
The purpose of this study is to facilitate the mesh generation of bone structures as needed by finite element calculations. The proposed technique uses several parallel cross-sectional scans of the bone unit investigated. Further application of a standard pattern recognition algorithm leads to homogeneous pixel partitions and physical outlines of each transversal section. These informations are exploited to generate interactively a threedimensional finite element mesh. Influence of some scanning parameters is discussed. Application of the described technique to femur discretization is also presented. ADVANCES
IN PHOTOELASTICITY
APPLIED
TO BIOMECHANICAL
PROBLEMS
R. BOURGOISand J. WAGNER (CIBO, Brussels, Belgium) Photoelasticity is one of the oldest experimental methods used in biomechanical research. In this way several fundamental ideas in the field of orthopaedics have been illustrated qualitatively by bidimensional photoelasticity. In spite of the advances in numerical stress analysis, the experimental stress analysis is currently very flourishing. Tridimensional photoelasticity has become a very interesting research tool in mechanics and civil engineering for complex problems of verifying computer programs; its application to biomechanical problems is possible, even to bone problems. Machining of bone models is impossible, therefore direct casting of the model is a must. Another important problem in two-dimensional and three-dimensional photoelasticity applied to biomechanical problems is the necessity to have photoelastic materials with different elastic moduli. Such materials may be manufactured by mixing different resins. The photoelastic and mechanical behaviour of these materials will be presented. ANALYSIS R. MOLLARD,
OF HUMAN
MOVEMENT
BY STROBOPHOTOGRAMMETRY
G. &NAZI and J. C. PINEAU (Laboratoire d’Anthropologie Appliquee et d’Ecologie Humaine, Laboratoire Associe 220 du C.N.R.S. Universite Paris V, France)
A three dimensional television system VICON (Oxford Dynamics) connected to a digital computer is used to achieve a biostereometric study of human movements.
STRUCTURAL
ANALYSIS
533
OF THE LOCOMOTOR
SYSTEM
V. NIKOLI~, M. HUDEC, M. MAROTTI, A. Jo and A. LOVRI~:(Department of Anatomy, Zagreb, Yugoslavia) Computerized tomography (CT) gives a quantified geometrical and structural picture of the cross-section of a body part, including muscles, tendons and ligaments. We investigated, by use of serial, transversal CT sections, the spatial distribution and position of the biomechanically important constituents on the living human locomotor system. Previously reported computer programs give the mechanically equivalent reduced bone crosssections and their moments of inertia. For certain positions and movements of the human body and extremities, the external forces can be determined quite accurately and, therefore, the internal resulting forces too. By a computerized structural analysis of a part of the extremity structure, we computed the tensile force intensities in muscles and tendons, and the adequate compressive forces in the bone, using the condition of the minimal internal energy. MINIMUM-VARIANCE ROTATION
ESTIMATION
IN JOINT BIOMECHANICS
OF INSTANTANEOUS
CENTRES AND AXES OF
FROM NOISY LANDMARK
MEASUREMENTS
H. J. WOLTRING, A. DE LANGE and R. HUISKES (Laboratory for Experimental Orthopaedics, University of Nijmegen, The Netherlands) The planar centre and spatial axis of rotation are useful quantifiers of biomechanical joint movement since they enable us to relate joint kinematics to joint geometry; furthermore, they allow the definition of suitable reference points for net joint moment assessment in dynamic movement studies. The instantaneous centre and axis of rotation (ICR and IAR, respectively) have usually been estimated from theirfinite counterparts; these are excessively sensitive to errors in measured landmark co-ordinates. The present paper treats sampled landmark data as measurements on a continuous, bandwidth-limited movement process. Through suitable low-pass filtering and differentiation techniques, largely unbiased estimates of the ICR and IAR can be obtained with a substantially higher accuracy than would be feasible through traditional, finite approaches. COMPUTERIZED TOMOGRAPHY TO FINITE ELEMENT
AND PATTERN RECOGNITION ALGORITHM MESH GENERATION OF BONE STRUCTURES
J. P. COYE~E (Universite Catholique de Louvain, Louvain-la-Neuve,
AS AN AID
Belgium)
The purpose of this study is to facilitate the mesh generation of bone structures as needed by finite element calculations. The proposed technique uses several parallel cross-sectional scans of the bone unit investigated. Further application of a standard pattern recognition algorithm leads to homogeneous pixel partitions and physical outlines of each transversal section. These informations are exploited to generate interactively a threedimensional finite element mesh. Influence of some scanning parameters is discussed. Application of the described technique to femur discretization is also presented. ADVANCES
IN PHOTOELASTICITY
APPLIED
TO BIOMECHANICAL
PROBLEMS
R. BOURGOISand J. WAGNER (CIBO, Brussels, Belgium) Photoelasticity is one of the oldest experimental methods used in biomechanical research. In this way several fundamental ideas in the field of orthopaedics have been illustrated qualitatively by bidimensional photoelasticity. In spite of the advances in numerical stress analysis, the experimental stress analysis is currently very flourishing. Tridimensional photoelasticity has become a very interesting research tool in mechanics and civil engineering for complex problems of verifying computer programs; its application to biomechanical problems is possible, even to bone problems. Machining of bone models is impossible, therefore direct casting of the model is a must. Another important problem in two-dimensional and three-dimensional photoelasticity applied to biomechanical problems is the necessity to have photoelastic materials with different elastic moduli. Such materials may be manufactured by mixing different resins. The photoelastic and mechanical behaviour of these materials will be presented. ANALYSIS R. MOLLARD,
OF HUMAN
MOVEMENT
BY STROBOPHOTOGRAMMETRY
G. &NAZI and J. C. PINEAU (Laboratoire d’Anthropologie Appliquee et d’Ecologie Humaine, Laboratoire Associe 220 du C.N.R.S. Universite Paris V, France)
A three dimensional television system VICON (Oxford Dynamics) connected to a digital computer is used to achieve a biostereometric study of human movements.